Novel FeII/EDDS/UV/PAA advanced oxidation process: Mechanisms and applications for naproxen degradation at neutral pH and low FeII dosage

Abstract The application of the integrated FeII/EDDS/UV/PAA (FEUP) process (EDDS = ethylenediamine-N,N’-disuccinic acid; PAA = peracetic acid) as a novel advanced oxidation process (AOP) for the degradation of a model contaminant, namely, naproxen (NAP), at neutral pH was investigated. The enhanced NAP degradation in this system at pH 7 was primarily attributable to the continuous activation of PAA via the UV-assisted FeII/FeIII cycle. A four-phase conceptual process of NAP degradation was established. The instantaneous degradation stage (IDS), in which FeII and PAA instantaneous react within 1 s, resulted in the degradation of ∼20% of NAP. The rapid degradation stage (RDS), in which the regenerated FeII rapidly activates PAA to produce the hydroxyl radicals (•OH) and organic radicals including CH3C(O)O•, CH3C(O)OO•, CH3OO• and •CH3 (defined as R-C•) without being scavenged by the FeII/FeIII-EDDS complexes, contributed to the degradation of ∼55% of NAP. The slow degradation stage (SDS), during which FeII/FeIII-EDDS complexes started competing for radicals, and resulted in the degradation of ∼15% of NAP. The continuous degradation stage (CDS), in which hydrogen peroxide (H2O2) was the only oxidant because PAA was exhausted, corresponded to the degradation of another ∼10% of NAP. The effect of water matrices including Cl-/Br-, HCO3-/CO32-, and humic acid (HA) was evaluated: Br-, HCO3-/CO32-, and HA exhibited an inhibiting effect on NAP degradation, while Cl- showed no influence on NAP degradation in the FEUP process. A superior degradation performance was achieved under a low FeII dosage and neutral conditions, demonstrating the great potential of the FEUP process for practical applications.